1. Field of the Invention
The invention relates to systems which analyze threaded joints and more specifically, to systems which use X-rays to observe the joint after assembly.
2. Description of the Prior Art
As it has become necessary in the past few years to drill deeper wells to obtain oil, the need for high yield strength casing and production tubing and strong connections between the various segments of the casing and the production tubing has increased. Testing of the pipe tube body forming the casing and tubing is generally done at the mill site and at the point where the pipe tube is to be threaded. At the threading location, various tests are performed to ensure that the threads meet design parameters. Additionally, hydrostatic pressure testing to approximately 80% of the strength of the pipe is generally performed. After the pipe is lowered into the well bore, in some instances a pressure test is performed with the pipe in tension, thus simulating certain well conditions and allowing a level of confidence to be developed after the pipe is in place.
It was eventually determined that over 50% of the downhole pipe failures occurred in the area of the connection for one of several different reasons. Therefore, there was significant attention focused on developing new types of connections with different thread parameters to help resolve significant numbers of these problems. Various other systems were developed to help make sure that a joint was properly made up or completed. In one of these systems, a computer system counted the number of turns the pipe member was making while measuring the torque applied to help ensure that the joint was properly made up. Speed control systems were developed so that the proper speed of assembly was used to help make up the joints. An alternate method used applied a mixture of inert gas such as nitrogen and helium to the connection area under pressure after the pipe was inserted into the well bore.
While these various systems were improvements over the prior systems, they still do not necessarily determine whether a joint is properly made up. The various pipe dopes, which are used to lubricate the joint during assembly, may be a major source of the leak after a period of time. The dope may first initially hide or seal a gap so that the various pressure-based techniques do not uncover the problem, but a leak eventually occurs because of the continuous pressure exerted when the pipe is inserted downhole. The masking ability and time to failure depend on the dope particle size and density.
The various tests currently performed before joint make up do not insure proper joint make up, but only that the individual parameters may be correct. Other methods utilized, such as the computerized system for measuring the number of turns and torque applied, are only indirect measurements and require relatively complicated assembly steps which increase the time required for a given operation and therefore the expense of drilling and developing the well. While the pressure testing provides a method for determining whether the complete pipe string is acceptable, should a failure be determined when the pipe is downhole, the entire string must be pulled to the point of flaw, thus necessitating a large expenditure and the increased possibility that the remaining joints which would then have to be remade could then be improperly formed.
U.S. Pat. No. 4,542,520 discloses a system for determining alignment of the hemispheres forming an inner sphere without disturbing an outer sphere. An X-ray beam is passed tangentially through the area of the hemisphere juncture. The patent discloses that the alignment is extrapolated from the curvatures of the hemispheres outside the seam weld because the exact junction can not be viewed.
U.S. Pat. No. 4,694,479 discloses a weld inspection system. An X-ray image from each of two different X-ray sources is made of a single weld from different angles. The images of the test weld are compared with the standard images of a perfect weld by an image comparator, which in turn produces a signal related to the quality of the comparison. A special-purpose computer determines the three dimensional coordinates of any defects.